Conventionally, in an internal-combustion engine such as an automobile engine, a plasma ignition apparatus is proposed that supplies, for the expansion of a plasma region, a high frequency to a spark discharge as a core of the plasma to ignite an air-fuel mixture. Herein, the spark discharge is generated in a combustion chamber by using an ignition plug.
For example, Japanese Laid-open Patent Publication No. 2010-001827 discloses a plasma ignition apparatus that includes an ignition plug that generates a spark discharge, a microwave oscillator that generates a microwave, and an antenna that radiates the microwave generated by the microwave oscillator into a combustion chamber.
In the Japanese Laid-open Patent Publication No. 2010-001827, the microwave oscillator includes a generation unit that generates a microwave and an amplification unit that amplifies the microwave, and these units are integrally housed in a housing that blocks the microwave.
However, a technology described in the Japanese Laid-open Patent Publication No. 2010-001827 has room for improvement in saving space. This is because there is a possibility that installation of the microwave oscillator integrally including the generation and amplification units may be difficult in such a case that installation space is limited as in, for example, an engine room of an automobile.